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I love the game, Secret Square , and have been really lucky to come across one of them on the used market. They aren't readily available as far as I can tell. However, there is a real simple way to reinvent this game if you have access to flashcards with different objects on them. Last year I did rhyming words with my students and used these cards. The cards don't need to have words on them. It is also good to have a variety of items in your cards like foods, animals, household objects, etc. I can now take those cards and play a version of Secret Square with them.
Basically, you lay out a bunch of cards and put a small, flat plastic chip under one of the cards. {Or for that matter you could use a small piece of construction paper.} Students then ask yes/no questions to try to figure out which item you have chosen. So, for example, if a student asks, "Is it red?" and the answer is "no", you then remove all the cards that are red. If the answer is "yes", then you remove the cards that have no red on them. {TIP: The person who hid the chip should be the only one touching the cards. I have found that the guessers may mistakenly pick up the card with the hidden chip if you allow them to start removing cards.} Questions continue to be asked until one of the students figures out which item has the hidden chip.
Here are some questions that students could ask in the target language...
Is it alive?
Is it red {or another color}?
Is it an animal?
Is it {Fill in the blank with an adjective}?
Is it a fruit?
Can it walk?
Can it fly?
As you can see there are all kinds of questions students can use depending on the pictures you have. It is more challenging the more cards you place on the table. My students enjoy the game more if there are over 25 cards. Another way to do this game is for the teacher to ask questions instead of the students. I tend to play it both ways with my students.
Have fun guessing!